The invention relates to an electrical circuit breaker with self-expansion and rotating arc, housed in a sealed casing filled with an insulating gas with high dielectric strength, notably sulphur hexafluoride, and comprising an arc extinction device arranged in a first extinguishing chamber, capable of communicating by means of exhaust channels with a second adjacent expansion chamber, said arc extinction device of each pole comprising :
a system of separable contacts having a movable arcing contact part mounted with sliding in the first chamber and capable of cooperating in the closed position with a fixed or semi-fixed arcing contact part,
a magnetic blow-out coil arranged in the first chamber to generate a magnetic field in the breaking zone, causing rotation of the arc when the arcing contact parts separate,
communication ducts inside the hollow arcing contact parts to constitute said exhaust channels for the compressed gas from the first chamber to flow to the second expansion chamber,
and an electrode to pick up the electrical arc in the breaking zone.
In a state of the art circuit breaker of the kind mentioned, the arc pick-up electrode is adjoining the front face of the coil, and the tubular fixed or semi-fixed arcing contact is set back from the electrode inside the coil. Switching of the arc onto the electrode causes the blow-out coil to be energized after the contacts have separated. The arc centering effect due to the action of the field is accentuated by the air blow-out during the phase in which the gases escape through the communication ducts between the extinguishing chamber and the expansion chamber. This results in a possibility of the arc root anchored on the electrode restriking on the fixed arcing contact, causing almost total shunting of the coil. The decrease of the magnetic field in the arcing zone causes the rotation of the arc roots to stop. Extinction of the arc is then jeopardized.
The coil generally has the total arcing current flowing through it when a short-circuit occurs causing a strong magnetic field in the breaking zone. Too fast rotation of the arc due to the action of this field may impede cooling of the arc.
The object of the invention consists of achieving a circuit breaker with self-expansion and rotating arc having a reliable arc extinction device, without the risk of the magnetic blow-out coil being de-energized.